Initial infections of chicken embryos with one million parasites of Plasmodium gallinaceum from a chicken infected by introduction of sporozoites resulted in avirulent infections, abberations in morphology of parasites and loss of gametocytes. Avirulence changes to virulence after five direct passages from chicken to chicken. Efforts are to be continued to determine the role of various hemoglobins in the ability of this malaria parasite to survive in this exotic environment and to determine the feasibility of instituting an avirulent, immunogenic parasite in the neonate chicken by complete adaptation in the embryo. Annual reinfection of perennial Asclepias of the United States by the Trypanosomatidae, Phytomonas elmassiani, is brought about by the existence of the protozoan in the migratory hemipteron, Oncopeltus fasciatus. Continued surveys to determine the prevalence of this parasite in plants and insects will be continued. Establishment of colonies of Drosophila melanogaster infected with Herpetomonas has provided a method of studying the dynamics of population parasitemia. Extended observations under rigidly controlled conditions should provide a basis for studies of the effects of environment on development of parasitemias in populations.